1. Field of the Invention
The invention relates to a process for preparing aromatic compounds having at least one chlorinated side chain by photochlorination of an aromatic compound having at least one alkyl group as a side chain and a method for stabilizing aromatic compounds having at least one chlorinated side chain.
Since aromatic compounds having a chlorinated alkyl side chain or chains, which may be produced by photochlorinating aromatic compounds having an alkyl side chain or chains, have a reactive chlorine atom at the side chain, said compounds are useful as intermediate materials. For example, .alpha.- monochloroxylene or .alpha.,.alpha.'-dichloroxylene, which may be produced by the photochlorination of xylene, can be easily converted to diglycols as raw materials for synthetic resins, diamines as raw materials for nylons and the like. Benzyl chloride, which may be prepared by photochlorinating toluene, can be used as an intermediate for the preparation of benzyl alcohol and the like.
2. Description of the Prior Art
When stainless steel materials are used for reactors in the photochlorination reaction of aromatic compounds having alkyl side chains, iron chloride and the like are formed in the reaction system and cause the production of a lot of nuclear substituted chlorinated products and resinous materials as by-products resulting in a remarkable decrease in yield of the end products, i.e. side chain chlorinated products.
Therefore, heretofore stainless steel materials have not been used, and reactors made of non metallic materials such as glass lined reactors and the like have been used for photochlorinating reactions. In general, the equipment cost of non-metallic materials are so expensive as compared with stainless steel materials that such non-metallic material reactors are not commercially advantageous.
For purposes of solving the problems, various methods have been proposed. For example, it is proposed to use additives such as triallyl phosphates, acetamide, urea, alkyl substituted amides, but these do not give a satisfactory result. U.S. Pat. No. 2,844,635 discloses a halogenating method comprising adding 0.1-10% by weight of alkylene polyamines, but according to the result of the present inventors' investigation, when such a large amount of alkylene polyamines as mentioned in said U.S. Patent is used in a reactor having a stainless steel material, the reaction liquid becomes less transparent and light reaches the inside of the system with difficulty so that, on the contrary, nuclear substituted products are produced in a large amount as by-products, and moreover, stainless steel materials are corroded at a temperature of 120.degree. C. or higher.
In addition, alkylene polyamines easily produce addition products by the reaction with hydrogen chloride as a by-product in the chlorinating reaction The resulting addition products can not effectively suppress the side reactions and therefore this is not a useful method. In view of the foregoing, there is not an effective countermeasure to the drawbacks in the photochlorinating reaction of aromatic compounds having an alkyl side chain or chains. Further, when for example, .alpha.-monochloroxylene. benzyl chloride or the like, which may be produced by photochlorinating reactions as above, are allowed to stand, the compounds deteriorate to generate hydrochloric acid and change to resinous materials. The phenomena are particularly remarkable when the temperature is high or metals such as iron, zinc and the like are present, and adversely affect production, purification and storage of .alpha.-monochloroxylene. For the purposes of solving the problems, methods for the stabilization by adding amines have been researched. For example, Japanese Patent Laid Open No. 66575/1973 discloses a method of distilling chlorinated xylene or toluene in the presence of an amine such as triethylamine, methyl diethylamine, tripropylamine, tributylamine, aniline, mono- and dialkylaniline, benzylamine, 2,2-dipyridine and the like, alkaline metal salts of aminocarboxylic acids, alkaline metal salts of hydroxycarboxylic acids or alkaline metal salts of condensed phosphoric acids, but these compounds do not give a satisfactory effect.
In addition, in order to solve such problems, Japanese Patent Laid Open Nos. 250329/1988 and 250330/1988 disclose a method of adding stabilizers mainly composed of hexamine. Though hexamine exhibits an excellent stabilizing effect, it was found that hexamine accelerates the corrosion of stainless steel apparatuses or machines when it is kept at an elevated temperature for a long period of time together with .alpha.-monochloroxylene or reaction products of chlorination of xylene containing .alpha.-monochloroxylene in stainless steel apparatuses or machines.
As mentioned above, at present there is not a method of stabilizing effectively, for example, .alpha.-monochloroxylene, benzyl chloride or the like, which may be produced by the photochlorination of aromatic compounds having an alkyl group as a side chain.